Validity and Sensitivity of Extended Field‐of‐View Wireless Palm‐Sized Ultrasonography for Assessing Muscle Hypertrophy

This study evaluated the validity and sensitivity of an extended field‐of‐view (EFOV) wireless palm‐sized ultrasound device for assessing quadriceps femoris cross‐sectional area (CSA), using magnetic resonance imaging (MRI) as the reference. Although previous studies have examined EFOV ultrasound, data validating EFOV wireless palm‐sized devices against MRI using large cohorts and training interventions have not been reported. In Experiment 1, midthigh CSA was measured in 100 young adults (75 males, 25 females) using ultrasound and MRI. Intra‐rater reliability was assessed via intraclass correlation coefficients (ICC), standard error of measurement (SEM), coefficient of variation (CV), and smallest detectable change (SDC). In Experiment 2, 11 males underwent an 8‐week resistance training program. Pre‐to‐post changes in CSA (ΔCSA) were compared between the two imaging modalities. In Experiment 1, the device demonstrated excellent reliability for males (ICC = 0.996; SEM = 0.85 cm 2 ; CV = 1.19%; SDC = 2.35 cm 2 ) and females (ICC = 0.993; SEM = 0.95 cm 2 ; CV = 1.73%; SDC = 2.63 cm 2 ). A strong correlation ( r = 0.98, p < 0.001) was observed between ultrasound and MRI, with a mean bias of −1.23 ± 2.70 cm 2 . In Experiment 2, both modalities detected significant hypertrophy ( p < 0.001). The mean ΔCSA measured by ultrasound (3.77 cm 2 , 5.98%) exceeded the SDC (2.35 cm 2 ). ΔCSA correlated strongly between modalities ( r = 0.92, p < 0.001). The EFOV wireless palm‐sized ultrasound device is a valid and sensitive tool for quantifying quadriceps femoris CSA and monitoring muscle adaptations, suitable for athletic performance and clinical settings.